|Relatives|| Leoric (father)|
|Appearances|| Diablo I (Warrior)|
Aidan is the hero of Diablo I, the Dark Wanderer and the son of king Leoric. He was the host of Diablo for the entirety of Diablo II and is one of the most pivotal characters in the lore. He was finally killed at the end of Diablo II, though it is uncertain how much of his humanity remained at that point.
Aidan lived with his father as he grew up. The earliest information we have about him is that he served in his father's army and was under the command of Lachdanan when he led the assault against Westmarch prior to the events of Diablo I. Upon returning to Tristram and seeing his father raised from the dead, his younger brother missing and Lazarus gone, he journeyed into the depths of the labyrinth under the Cathedral.
The further down he'd gotten however, the larger Diablo's influence over him had grown. The Lord of Terror recognized what a fine host Aidan would make, and so slowly crept into his mind. Once Diablo was slain, Aidan had become convinced that in order to contain Diablo he had to shove the soulstone into himself, and so Aidan became the Dark Wanderer.
 The Dark Wanderer
As Aidan emerged victorious from the Cathedral, the townspeople of Tristram rejoiced. No one suspected his dark secret though save for Adria, with whom he is hinted to have conceived Leah during his brief stay in Tristram before he left for the east. Shortly after he left, demons poured forth from the cathedral and laid waste to the town, killing all remaining inhabitants save for Deckard Cain who was imprisoned and left to die.
On his journey east he came upon the Rogue Monastery and instructed his demon minions to lay waste to it before summoning Andariel to guard the mountain pass and any would-be pursuers. He then tracked down Marius, a survivor of the attack on the monastery. Why he did this, why he chose Marius and why Marius ended up following him is unknown, but the two began traveling towards Lut Gholein and the tomb of Tal Rasha where Baal was buried.
When the two find the tomb, Tyrael is waiting for them and engages Aidan in a fight to prevent him from freeing Baal. At this point Marius plays a pivotal role as he is the one to set Baal free (albeit unintentionally). Without his aid, it is likely that Tyrael would have won and prevented the return of the Three. Instead Tyrael is imprisoned and Duriel summoned to guard him.
As the journey progressed Aidan began to show more and more demonic features as Diablo solidifies his control, and it's questionable how much free will, if any at all, Aidan retains at this point. The last parts of him die when Diablo assumes his demonic form under Travincal in Kurast.